Contributors All the authors listed contributed significantly to the conception and design, or analysis and interpretation of data, the
drafting the article or revising it critically for important intellectual content and the final approval of the version to
be published.

Accepted 6 March 2012

Published Online First 19 April 2012

Abstract

Background Research has raised significant concern regarding the affective consequences of synthetic drug use. However, little evidence
from well-controlled longitudinal studies exists on these consequences. The aim of this study was to determine whether use
of meth/amphetamine (speed) and ±3,4-methylenedioxymethamphetamine (MDMA, ecstasy) is independently predictive of subsequent
depressive symptoms in adolescents.

Methods A sample of 3880 adolescents from secondary schools in disadvantaged areas of Quebec, Canada, were followed over time (2003–2008).
Logistic regression was used to test the association between meth/amphetamine and MDMA use in grade 10 (ages 15–16 years)
and elevated depressive symptoms on an abridged Center for Epidemiologic Studies-Depression scale in grade 11, controlling
for pre-existing individual and contextual characteristics.

Results After adjustment, both MDMA use (OR 1.7, 95% CI 1.1 to 2.6) and meth/amphetamine use (OR 1.6, 95% CI 1.1 to 2.3) in grade
10 significantly increased the odds of elevated depressive symptoms in grade 11. These relationships did not vary by gender
or pre-existing depressive symptoms. Increased risk was particularly observed in concurrent usage (OR 1.9, 95% CI 1.2 to 2.9).

Conclusions Adolescent use of meth/amphetamine and MDMA (particularly concurrent use) is independently associated with subsequent depressive
symptoms. Further enquiry must determine whether these associations reflect drug-induced neurotoxicity and whether adolescence
is a period of increased vulnerability to the hazards of synthetic drug exposure.

Footnotes

Funding This research was funded by a grant from the Fonds Québécois de Recherche sur la Santé et la Société (FQRSC, 2007-NP-112947).

Competing interests The authors have no conflict of interests to disclose. Funding organisations played no role in design and conduct of the
study; collection, management, analysis and interpretation of the data; and preparation, review or approval of the manuscript.
Authors had full access to all the data in the study and take responsibility for the integrity of the data and the accuracy
of the data analysis.

Patient consent Participant consent was obtained using another consent form.